1. Field of the Invention
The present invention relates to a headlamp or a foglamp for a vehicle in which the illumination surface of the beam is a laterally extending rectangular shape.
2. Description of the Prior Art
A rectangular type headlamp, simply speaking, is designed to have a rectangular shape when it is viewed from the front side, by cutting the top, bottom, right and left sides of a circular shape headlamp.
This kind of rectangular shape headlamp comprises three parts; a portion from which a light is radiated (lamp), a paraboloidal reflector and a front lens. As shown in FIG. 8, if the rectangular portion 2 being inscribed within a circle is utilized, the remaining portions A, B, C, and D are not utilized for radiation area, resulting in a dark lamp.
In order to prevent this decrease of quantity of light, the rectangular shape headlamp is generally designed, as shown in FIG. 9, to use a larger circular reflector 4 than the conventional circular shape reflector 3, by utilizing the rectangular portion 5 being inscribed within the circle 4. According to this design, the loss of the light from the top and bottom sides of the reflector can be compensated with a beam from the oblique line portions of left and right sides (the light which is conventionally not necessary to use in the circular shape). Also, a halogen lamp having the same consumed electric power and being brighter than the others, (the light quantity is increased to 30 to 40%) is used to prevent the decrease of light quantity of the headlamp.
A rectangular shape headlamp, as shown in FIG. 10(a), having an aspect ratio of about 1:1.4 to 1:2, is recently being used in order to reduce the air resistance of the vehicle and to raise the fuel consumption rate. From the design requirement, it is required to form the headlamp shape to be more slender in the horizontal direction. For the headlamp formed by cutting the top, bottom, left and right sides of the circular shape headlamp, as shown in FIGS. 10(b) and (c), as the shape becomes more slender, the more the ratio of the volume escaping in the upper and lower directions to the total volume from the lamp increases. Thus, for a lamp having the same consumed electric power, the decrease of the light quantity increasingly becomes large. Designing the lamp more slender is considered to be a difficult problem because of the efficiency improvement of the halogen lamp being almost to its limit.
In many highly styled cars, a design is adopted in which the lamp is enclosed inside of the bonnet when not in use during daytime and it is raised out from the bonnet when in use at night. But, the increase of air resistance during night driving is inevitable for this kind of design. Also, the design in which a plurality of small rectangular shape headlamps are arranged in line forming a set of the headlamps has been studied, but this design has problem in a maintenance, etc.